The long-established aqueous or solventborne coating materials, especially the basecoat materials, and the multicoat effect paint systems produced using them exhibit good performance properties.
The continually growing technical and, in particular, esthetic requirements of the market, however, and particularly the requirements imposed by the automakers and their customers, are necessitating continual onward development beyond the technical and esthetic level achieved to date. Modern bodywork design, with its pronounced rounded elements, is very much in harmony with paint finishes having a strong flip-flop effect. The desire to produce an effect that mimics metal can be realized through the use of very thin aluminum leaflets, with thicknesses in the nanometer range, as are described in EP 0826745 A2, for example.
In particular there is a need for new coating compositions which make it possible to produce basecoat systems that exhibit a particularly strongly pronounced light/dark behavior. At the same time, however, the advantages achieved through the known basecoat materials and the basecoat systems produced from them should not be lost, but instead should be retained at least to the same extent and preferably to a greater extent.
The corresponding effect basecoat systems and, where appropriate, color basecoat systems as well ought therefore to exhibit no haze and to possess good leveling and also a very good overall visual appearance. The basecoats ought further to be free from film defects, light/dark shading (clouds), and gel specks. Furthermore, the resulting coatings ought not to exhibit any optical defects and ought to possess satisfactory adhesion to the clearcoat.
The coating compositions are to be distinguished, further, by good storage stability, which means no significant deterioration in the properties either of the coating compositions themselves or of the coatings produced from these coating materials when the latter are stored at 40° C. (for 28 days). Whilst there should be no deterioration in the rheological properties of the coating compositions, in particular no increase in viscosity, and no gel speck formation and no impairment of the metallic flop.
Customary aqueous basecoat materials of the prior art are easy to prepare, stable on storage, and transportable. They meet the typical requirements of automotive finishing in terms of application, technological properties (adhesion, long-term weathering), storage stability, circulation stability, and appearance.
EP 1 591 492 A1 describes for example a basecoat material comprising metal pigments which can be aqueous or solvent-based and which contains a relatively high fraction of the metal pigment—preferably 12% to 20% by weight based on the total binder content. The focus of EP 1 591 492 A1, however, is to provide systems of maximum moisture stability.
WO 2006/017197 A1 discloses a process for producing special-effect finishes but uses relatively low fractions of a leaflet-shaped metal pigment in conjunction with comparatively high amounts of binder and comparatively high solids fractions in order to produce an effect coating material, the leaflet-shaped metal pigment being accompanied in the coating material by at least one further, additional special-effect pigment.
The metallic light/dark behavior (flip-flop) of solvent-based basecoat materials of the kind used, for example, for finishing wheel rims is nevertheless to date a long way from being attained when using prior-art aqueous basecoat materials comprising effect pigments.
Factors of importance for achieving a flip-flop effect include not only use of PVD aluminum leaflets as pigments in producing metallic paint, but also the precise harmonization of the amount of the further components in the aqueous paint system.
Aqueous coating materials based on polyacrylate and polyester binders and on amino resin crosslinking agents, and comprising a leaflet-shaped aluminum effect pigment produced by PVD methods (e.g., Metalure® from Eckart), are known, but cannot yet meet all of the requirements made on them.
The object on which the present invention is based was therefore that of providing new physically, thermally and physically, and thermally curable compositions which comprise metallic pigments, which are easy to prepare, and which meet all of the requirements of present-day aqueous vehicle paints. In addition they are to have a pronounced flip-flop effect.
The coating materials ought to be suitable in particular as aqueous basecoat materials for producing effect basecoats and color and effect basecoats of multicoat paint systems. In this context they ought to exhibit excellent application behavior and outstanding leveling.
Even in extremely thin coats and in comparatively low metallic pigment concentrations, the effect basecoats and color and effect basecoats ought to show high hiding power, outstanding intercoat adhesion, particularly high condensation resistance, isotropic pigment dispersion, an especially strongly pronounced light/dark behavior (metallic flop), and also very high metallic brilliance and very high gloss. At the same time they ought to be free from film defects, such as light/dark shading (clouds) and gel specks. All in all they ought to exhibit a mirror effect very much like that of chrome, and, if they have a coloring action, ought to have a particularly elegant, full color effect with minimal sparkle effect (glitter effect).